This application claims the benefit of priority under 35 U.S.C. xc2xa7119(a) of Taiwan Patent Application No. 090102986, filed Feb. 9, 2001
1. Field of the invention
The invention generally relates to optical drives and laser power control methods, and more particularly to a system and a method for Constant Angular Velocity control format.
2. Description of the Related Art
Among optical recording drives, control format for recording can be categorized into CAV (Constant Angular Velocity) and CLV (Constant linear Velocity) control formats. With CAV control format, a disk rotates at a constant speed regardless of what area of the disk is being accessed. Rotational speed of a spindle in the optical recording drive is constant. Data are recorded into tracks of an optical disk. Tracks are formed in a spiral line extending from the inner to the outer of an optical disk. On the other hand, the purpose of CLV is to ensure a constant data rate regardless of where on the disk the data is being accessed. With CLV, the rotation speed of the disk changes based on how close to the center of the disk the data is. For tracks near the center, the disk rotates faster, and for data on the outside, the disk rotates slower.
Current CD-ROM or CD-RW drive uses CLV control format for disk recording. Data is recorded at a uniform density with CLV control format onto a disk. As the high rotational speed of the spindle develops, CLV control format cannot cope with the demands come with high rotational speed. A recent development utilizing a CAV control format recording, whereas disk data recording performance approximates to the resulted uniform density from CLV control format recording. For example, for an optical drive under 16 times CLV control format, the rotational speed of inner tracks is 800 rpm. In contrast, for an optical drive using 16 times CAV control format recording, performance of the outer tracks recording can be as high as the performance gained from an optical drive using 40 times CLV control format recording.
In order to cope with the spindle operation adapting a CAV control format, two technical problem must be resolved: one is laser power has to be subject to the linear velocity changes, the other is recording pulse has to be subject to the linear velocity changes of a disk.
To realize the above-described technologies, the invention discloses a system and method for laser power control. The system and method is used for CAV (Constant Angular Velocity) control format recording, whereas the existing disk data is recorded under CLV (Constant linear Velocity) control format recording. The system according to the invention comprises: a spindle, a spindle control, a PUH (pick-up head), a laser driver, an automatic power control, a write pulse generator, a clock synthesizer, an ATIP (Absolute Time In Pre-grooves) decoder, a CLV value detector, a laser power control, and a dynamic write strategy table.
The spindle takes control of rotating of an optical disk with CAV control format via the spindle control. The PUH is used for reading/recording data from/onto an optical disk. The laser driver is used for generating and outputting a laser driver signal to the PUH. When the PUH receives a laser driver signal, it generates a feed signal and a wobble signal, the wobble signal reflected by the optical disk and then read by the PUH. The feed signal is received by the automatic power control; thereafter the automatic power control generates a first control signal used for causing the laser driver to adjust the laser driver signal. After the ATIP decoder receives the wobble signal, the ATIP decoder generates and outputs ATIP decoded data to the CLV value detector. The CLV value detector receives ATIP decoded data and generates a CLV decoded data to the laser power control. The laser power control receives the CLV decoded data and generates a second control signal, which is used for causing the automatic power control to adjust the first control signal.
With the clock signal provided by the clock synthesizer, the write pulse generator generates a write pulse signal to control the laser driver signal of laser driver. The dynamic write strategy table also receives CLV decoded data and then generates a third control signal for causing the write pulse generator to adjust the write pulse signal.
The dynamic write strategy table comprises: a CLV value detector, a decoder and a recorded medium. The CLV value detector is used for receiving the CLV decoded data, determining a CLV value of the CLV decoded data is within a fixed range and generating a CLV value signal. Wherein, the CLV value signal comprises an index value representing the fixed value range. The decoder receives the CLV value signal and as a result generates a corresponding address signal. The recorded medium is used for recording a plurality of write strategy patterns. Each write strategy pattern corresponds to an address signal and thereafter generating a corresponding third control signal. The CLV value detector comprises a matrix used for determining the fix value range corresponding to the CLV value. Wherein the CLV value detector can be either software or hardware. In addition, the recorded medium can be performed by a SRAM (Static Random Access Memory).
In the above-described system, the ATIP decoded data comprises predetermined absolute time in pre-grooves and biphase clock, wherein the biphase clock is used to cause clock synthesizer to generate a clock signal. The CLV decoded data comprises a CLV value resulted from disk real-time rotating. The CLV value equals to the count of the biphase clock detected by the CLV value detector at the fixed time interval. In addition, the second control signal comprises a laser recording power value corresponding to the CLV value. The laser power value can be set as a fixed value. The fixed value can be gained from an optimized value in experiments.
According to prior art system, the disk inner track area comprises a PCA (Power Calibration Area), where a laser power calibration such as an OPC (Optimal power Calibration) occurring. The present invention provides an alternative, an external laser PCA, which is on the second half of the lead out area on the outer track area. Wherein the external laser PCA is divided into 100 units. Each unit is divided into 15 blocks, which are used for providing laser power control for performing an OPC.
When the spindle is under fixed CAV control format, a linear equation for optimized laser recording power is generated from interpolation, which is used for calculating an optimized laser recording power with desired CLV value. An OPC in the PCA is performed and renders an optimized laser recording power of the inner track area of the disk. At the same time, the CLV value detector detects a CLV value of the inner track area. In the same way, an OPC in the PCA is performed and renders an optimized laser recording power of the outer track area of the disk. The CLV value detector detects another CLV value of the inner track area. Accordingly, using interpolation with the two sets of CLV values and corresponding optimized laser recording power from the OPC in the PCA in the inner and outer track, a linear equation for optimized laser recording power is generated.
In addition, when the spindle is under variable CLV control format, a linear equation for optimized laser recording power is generated by extrapolation. At first, set the spindle under a first fixed multiple CLV control format. An OPC in the PCA is performed and renders an optimized laser recording power of the inner track area of the disk. At the same time, the CLV value detector detects a CLV value of the inner track area. Then, set the spindle under a second fixed multiple CLV control format. Similarly, an OPC in the PCA is performed and renders an optimized laser recording power of the inner track area of the disk. At the same time, the CLV value detector detects a CLV value of the inner track area. Accordingly, using extrapolation with the two sets of CLV values and corresponding optimized laser recording power from the OPC in the PCA in the inner track under the first and the second multiple CLV control format, a linear equation for optimized laser recording power is generated.